1. Field of the Invention
The present invention relates to an image sensor unit, an image reading apparatus, and an image forming apparatus. Particularly, the present invention relates to an image sensor unit, an image reading apparatus, and an image forming apparatus that read large originals and the like.
2. Description of the Related Art
Readable lengths (hereinafter, “read lengths”) of originals are generally about A4, B4, and A3 sizes in an image sensor unit used in an image reading apparatus, such as a facsimile and a scanner. In recent years, an elongated image sensor unit that can read large originals in A2, A1, and A0 sizes exceeding the read length of A3 size is used in an image reading apparatus, such as an electronic white board.
In the image sensor unit of the image reading apparatus that reads large originals and the like exceeding the A3 size, a plurality of sensor substrates shorter than the A3 size, on which a plurality of sensor chips are mounted, are arranged in series in a main-scan direction. In the serial arrangement of the sensor substrates, it is ideal to extremely reduce intervals between the sensor chips mounted on adjacent sensor substrates to reduce image missing sections in reading. However, high reading accuracy is not demanded in the image sensor unit used for an electronic white board or the like, and there is no problem even if the intervals between the sensor chips are large.
On the other hand, the same read quality as that of a general scanner is demanded in an image reading apparatus that needs fine reading of a large map and the like, and generation of an image missing section needs to be prevented. For example, Patent Document 1 discloses a photoelectric conversion apparatus elongated by connecting a plurality of wiring boards (sensor substrates) on which LED chips (sensor chips) are arranged.
Patent Document 1
Japanese Laid-open Patent Publication No. 7-086541
In the photoelectric conversion apparatus disclosed in Patent Document 1, the sensor chips protrude from ends of the sensor substrates to arrange the sensor chips at equal intervals in a main-scan direction when adjacent sensor substrates are connected. To connect the adjacent sensor substrates, accuracy in a sub-scan direction is required in addition to accuracy in the main-scan direction. More specifically, the sensor chips need to be arranged at equal intervals in the main-scan direction, and the sensor chips need to be arranged without deviation in the sub-scan direction. However, alignment (positioning) in the sub-scan direction is not taken into account in the photoelectric conversion apparatus, and the alignment of the sensor chips is not easy.